Nuclear Modification Factor for Charged Pions and Protons at Forward Rapidity in Central Au+Au Collisions at 200 GeV

We present spectra of charged pions and protons in 0-10% central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at mid-rapidity ($y=0$) and forward pseudorapidity ($\eta=2.2$) measured with the BRAHMS experiment at RHIC. The spectra are compared to spectra from p+p collisions at the same energy scaled by the number of binary collisions. The resulting nuclear modification factors for central Au+Au collisions at both $y=0$ and $\eta=2.2$ exhibit suppression for charged pions but not for (anti-)protons at intermediate $p_T$. The $\bar{p}/\pi^-$ ratios have been measured up to $p_T\sim 3$ GeV/$c$ at the two rapidities and the results indicate that a significant fraction of the charged hadrons produced at intermediate $p_T$ range are (anti-)protons at both mid-rapidity and $\eta = 2.2$

The Shear Viscosity to Entropy Density Ratio of Trapped Fermions in the Unitarity Limit

We extract the shear viscosity to entropy density ratio \eta/s of cold fermionic atoms in the unitarity limit from experimental data on the damping of collective excitations. We find that near the critical temperature \eta/s is roughly equal to 1/2 in units of \hbar/k_B. With the possible exception of the quark gluon plasma, this value is closer to the conjectured lower bound 1/(4\pi) than any other known liquid.Comment: published versio

Recent results from BRAHMS

The BRAHMS collaboration ended its data collection program in 2006. We are now well advanced in the analysis of a comprehensive set of data that spans systems ranging in mass from p+p to Au+Au and in energy from $\sqrt{s_{NN}} = 62.4$ to 200 GeV. Our analysis has taken two distinct paths: we explore the rapidity dependence of intermediate and high-transverse-momentum, identified-particle production, thus helping to characterize the strongly-interacting quark-gluon plasma (sQGP) formed at RHIC; we also explore particle yields at lower transverse momentum to develop a systematic understanding of bulk particle production at RHIC energies.Comment: 8 pages, 5 figures, presented at the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur, India, February 4-10, 200

Gluon shadowing in the Glauber-Gribov model at HERA

We calculate shadowing using new data on the gluon density of the Pomeron recently measured with high precision at HERA. The calculations are made in a Glauber-Gribov framework and Pomeron tree-diagrams are summed up within a unitarity-conserving procedure. The total cross section of \vphot A interaction is then found in a parameter-free description, employing gluon diffractive and inclusive distribution functions as input. A strong shadowing effect is obtained, in good agreement with several other models. Impact parameter dependence of gluon shadowing is also presented.Comment: 18 pages, 6 figures; references added, discussion of model enlarged, calculation of low-x contribution corrected; to appear in Phys. Let

Gluon shadowing and unitarity effects

New data from HERA experiment on deep inelastic scattering have been used to parametrize nucleon and Pomeron structure functions. Within the Gribov theory, the parameterizations were employed to calculate gluon shadowing for various heavy ions. The latter was compared with predictions from other models. Calculations of multiplicity reduction due to gluon shadowing for d+Au collisions at forward rapidities at $\sqrt{s}$=200 GeV are in good agreement with BRAHMS data on the nuclear modification factor.Comment: 5 pages, 4 figures, submitted to Acta Physica Hungarica A, Quark Matter 2005 poster session proceedings; minor changes in the text adde

Modeling the jet quenching, thermal resonance production and hydrodynamical flow in relativistic heavy ion collisions

The event topology in relativistic heavy ion collisions is determined by various multi-particle production mechanisms. The simultaneous model treatment of different collective nuclear effects at high energies (such as a hard multi-parton fragmentation in hot QCD-matter, thermal resonance production, hydrodynamical flows, etc.) is actual but rather complicated task. We discuss the simulation of the above effects by means of Monte-Carlo model HYDJET++.Comment: Talk given at Workshop "Hot Quarks 2010" (La Londe Les Maures, France, June 21-26, 2010); 4 pages including 2 figures as EPS-files; prepared using LaTeX package for publication in Journal of Physics: Conference Serie